Scavenging behaviour by Ergalatax contractus (Gastropoda: Muricidae) and interactions with Nassarius nodifer (Gastropoda: Nassariidae) in the Cape d’Aguilar Marine Reserve, Hong Kong

Aspects of the feeding behaviour of Ergalatax contractus (Muricidae) were studied. Field experiments demonstrated that large numbers of individuals of this species, comprising *90% of a suite of gastropod scavengers, were attracted to baited traps in the subtidal sands of Lobster Bay, Cape d’Aguilar Marine Reserve, Hong Kong. Laboratory experiments identi¢ed the e¡ective chemo-detection distances of E. contractus as 60 cm in still and 480 cm in £owing water, respectively. The average times to arrival at bait in still and £owing water were 92.3 and 69.0 min, respectively, but were signi¢cantly less for individuals experiencing a longer period of starvation. The mean time taken for E. contractus to consume a meal was 70.6min. Comparisons were made between Ergalatax contractus and Nassarius nodifer, representative of a suite of sympatric scavenging nassariids in Lobster Bay. The nassariid arrived signi¢cantly faster at bait in both still (30.2min) and £owing water (20.8min) than E. contractus and fed faster (25.7min), as is typical of representatives of the Nassariidae. Although the two species partition carrion resources temporally, manipulation experiments provided evidence for inter-speci¢c competition between them. That is, although E. contractus possesses the morphological and behavioural characteristics of a predator, its opportunistic scavenging abilities have led to its success and numerical superiority on the shallow subtidal sands of Lobster Bay. The dominance of E. contractus in Lobster Bay, and elsewhere in Hong Kong, is unusual. Here, the normally predatory E. contractus, far outnumbers all other scavengers, possibly because of an enhanced, largely allochthonous, supply of food which it is able to exploit by virtue of its previously identi¢ed opportunistic habit of scavenging the leftovers of other predators. The presence of inter-speci¢c competition between E. contractus and a sympatric suite of nassariids enhances, not impedes, carrion exploitation.